MAIDUGURI, Nigeria, Jan 27 (Thomson Reuters Foundation) - More than a year after she was taken from Boko Haram by the Nigerian army, Falta still has mixed feelings about her freedom.

While she does not miss life in the Sambisa forest - a vast former game reserve in northeast Nigeria and the jihadists' final stronghold - Falta is worried about her son, Mamman Nur, who is believed to be one of Boko Haram's leading commanders.

Nur was the suspected mastermind behind a suicide bomb on U.N. headquarters in the capital Abuja in August 2011 that killed 23 people. Nigeria's state security service has offered a $160,000 bounty for information leading to his capture.

The question of whether Boko Haram still has a base in the Sambisa is disputed, with President Muhammadu Buhari last month saying their last enclave in the forest was captured, before a man purporting to be the militants' leader denied the claim.

Falta, a frail grandmother who describes herself as an 'old woman', recalled how her son insisted that his entire family move to the Sambisa for their safety following clashes between Boko Haram and the army in their hometown of Banki.

With no-one else to look after her, Falta said she had no choice but to go with her son, his three wives and his children to the base from which the militant group has waged a bloody seven-year campaign to create an Islamic state in the northeast.

"He is my only remaining child ... his father died when he was a child," said Falta, who had been a farmer in Banki.

Despite her doubts, life in the Sambisa was comfortable for Falta. Vans arrived regularly with food and clothes, a hospital staffed with doctors and nurses tended to the ill, and Falta had her own room in a house she shared with her son and his wives.

"I was happy to have my grandchildren around me," she said.

NOWHERE TO GO

Falta lived with her son for more than four years before she and his wives were captured by the Nigerian military in a 2015 raid on the Sambisa forest that took place while Nur was away.

Sitting on a mat in the government safe house, Falta said she had repeatedly tried to talk her son out of joining the Islamist militant group, which has killed some 15,000 people and forced more than two million to flee their homes since 2009.

"But he did not listen to me," Falta said, explaining that she does not know when or why her son joined the jihadists. "I gave birth to him, but I did not give birth to his lifestyle."

"After he moved to the Sambisa, I decided it was no longer any use talking ... I could see he was already deeply involved."

President Buhari in December said Boko Haram's last enclave in the forest had been captured in the "final crushing" of the group, yet the Thomson Reuters Foundation has been unable to independently verify that the area was captured.